Comparison of the low-speed frictional characteristics of silicon nitride and steel balls using conventional lubricants

The friction behavior of Si3N4 ceramic balls operating under ultra-low-speeds with velocity reversal is investigated. Twenty-one sets of exclusively ultra-low-speed operating conditions were examined that include rotational speeds in the range of .01-1 deg/s, normal loads varying from 81.6 to 185.4 N per ball, and two conventional lubricants: DTE 24 and SAE 20 oil. General trends for the friction torque behavior of ceramic balls were established. Theoretical expressions and empirical correlations are presented for evaluation of the steady torque, T-s, and the rest slope, sigma. These relationships can be used in Dahl's model to completely characterize the hysteresis friction behavior of ceramic balls. The results of the ceramic ball friction measurements were compared to that of steel balls operating under identical conditions. In addition, a series of experiments was conducted to extend the operating speeds from .01-500 deg/s. Under the conditions tested the lubrication regimes from boundary to fluid-film were identified.